Production of a semiconductor device involves a step of forming an electroconductive film on the surface of a wafer to form a wiring layer by photolithography, etching etc., a step of forming an interlaminar insulating film on the wiring layer, etc., and an uneven surface made of an electroconductive material such as metal and an insulating material is generated on the surface of a wafer by these steps. In recent years, processing for fine wiring and multilayer wiring is advancing for the purpose of higher integration of semiconductor integrated circuits, and accordingly techniques of planarizing an uneven surface of a wafer have become important.
As the method of planarizing an uneven surface of a wafer, a CMP method is generally used. CMP is a technique wherein while the surface of a wafer to be polished is pressed against a polishing surface of a polishing pad, the surface of the wafer is polished with an abrasive in the form of slurry having abrasive grains dispersed therein (hereinafter, referred to as slurry). As shown in FIG. 1, a polishing apparatus used generally in CMP is provided for example with a polishing platen 2 for supporting a polishing pad 1, a supporting stand (polishing head) 5 for supporting a polished material (wafer) 4, a backing material for uniformly pressurizing a wafer, and a mechanism of feeding an abrasive. The polishing pad 1 is fitted with the polishing platen 2 for example via a double-sided tape. The polishing platen 2 and the supporting stand 5 are provided with rotating shafts 6 and 7 respectively and are arranged such that the polishing pad 1 and the polished material 4, both of which are supported by them, are opposed to each other. The supporting stand 5 is provided with a pressurizing mechanism for pushing the polished material 4 against the polishing pad 1.
Conventionally, such polishing pads are produced by batch methods such as (1) a method including pouring a resin material into a mold to form a resin block and slicing the resin block with a slicer; (2) a method including pouring a resin material into a mold and pressing the resin material into a thin sheet form; and (3) a method including melting a resin material as a raw material and directly extruding the resin material from a T die into a sheet form. For example, Patent Document 1 discloses that polishing pads are produced by reaction injection molding.
Laminate polishing pads are produced by laminating, with an adhesive or double-side tape, a plurality of resin sheets, such as a polishing layer and a cushion layer, obtained by the method described above, and such a method for production of laminate polishing pads has the problems of a large number of production steps and low productivity rate. Patent Document 2 discloses that in order to solve the problems, laminate polishing pads are produced using an extruder.
A method for continuous production of a polyurethane/polyurea polishing sheet is proposed in order to prevent variations in hardness, gas cell size or the like, which would be caused by batch production methods (see Patent Document 3). Specifically, the method includes mixing a polyurethane material, a fine powder with a particle size of 300 μm or less and an organic foaming agent, ejecting the mixture between a pair of endless plane belts and casting the mixture, then subjecting the mixture to a polymerization reaction with heating means, and separating the resulting sheet-like product from the plane belts to obtain a polishing sheet material.
The polishing surface of polishing pads to be in contact with a substance to be polished is generally provided with grooves for holding and replacing a slurry. The polishing surface of polishing pads made of a foam has a large number of openings and thus has the function of holding and replacing a slurry. The polishing surface provided with grooves allows more efficient holding and replacing of a slurry and can prevent destruction of the polished substance, which is caused by adsorption on the polished substance.
As conventional polishing pads for use in high-precision polishing, polyurethane foam sheets are generally used. Polyurethane foam sheets are excellent in locally planarizing performance but have insufficient cushion performance, and therefore it is difficult to evenly apply a pressure to the entire surface of a wafer from such a polyurethane foam sheet. Thus, another soft cushion layer is generally provided on the back side of such a polyurethane foam sheet to form a laminate polishing pad for use in polishing processes. For example, the laminate polishing pads described below have been developed.
There is disclosed a polishing pad including: a laminate of a first relatively-hard layer and a second relatively-soft layer; and grooves with a certain pitch or projections with a certain form on the polishing surface of the first layer (see Patent Document 4).
It is also disclosed a polishing fabric including: a first sheet-like member having elasticity and irregularities on its surface; and a second sheet-like member that is provided on the surface of the first sheet-like member having irregularities and has a surface for facing the polished surface of an substrate to be treated (see Patent Document 5).
There is also disclosed a polishing pad including a polishing layer and a supporting layer that is laminated on one side of the polishing layer and made of a foam having a compression ratio higher than that of the polishing layer (see Patent Document 6).
However, the conventional laminate polishing pads have a problem in which since they are produced by bonding the polishing layer to the cushion layer with a double-side tape (a pressure-sensitive adhesive layer), a slurry can intrude between the polishing layer and the cushion layer during polishing to reduce the adhesion of the double-side tape so that the polishing layer can be detached from the cushion layer. When the surface of such laminate polishing pads are provided with grooves, there is also a problem in which abrasive grains in a slurry, polishing dust and the like tend to stay in the grooves to cause groove clogging so that the polishing speed can be reduced or made unstable and the planarity or in-plane uniformity of the polished substance can be reduced.                Patent Document 1: Japanese Patent Application Laid-Open (JP-A) No. 2004-42189        Patent Document 2: JP-A No. 2003-220550        Patent Document 3; JP-A No. 2004-169038        Patent Document 4: JP-A No. 2003-53657        Patent Document 5: JP-A No. 10-329005        Patent Document 6: JP-A No. 2004-25407        